A time series study of anti-diarrheal drug sales and tap-water quality

The City of Le Havre in France operates two water treatment plants and dist ributes water to 200,000 people. It exploits, as the sourer of its drinking water, karstic resources that are subjected to episodical microbiological quality degradations. The first plant only chlorinates the water, whereas t he second plant normally uses direct sand filtration before chlorination bu t can also implement coagulation-settling when turbidity of the raw water e xceeds 3 nephelometric turbidity units (NTU). During the study period there were several occurrences of failure to maintain residual chlorine as well as significant turbidity increases. The treated water still met all microbi ological criteria fur potable water in France and this study was undertaken to determine if public health was adequately protected. An ecological time series study was carried out on data collected between April 1993 and Sept ember 1996. The record of the sales of medications prescribed or self-selec ted for the treatment of gastroenteritis (GE) were provided by the pharmaci sts participating in the epidemiological surveillance network of Le Havre. Sales data, residual chlorine and turbidity measurements were analyzed. Int erruption of chlorination of the unfiltered water resulted in a significant increase of medication sales 3 to 8 days later. Raw water turbidity increa ses resulted in increases of medication sales during the 3 following weeks. The data analyzed suggest that about 10% of the annual cases of gastrointe stinal illnesses could be due to the consumption of tap water. This annual average does not reflect the proportional attributable risk occurring durin g specific periods and underscores the fact that current regulations still do not provide complete protection of public health. Furthermore, such fail ures have the potential of causing major GE outbreaks if raw water microbio logical quality degrades significantly after rainfall events.